Off-road machines for felling trees and for handling felled trees ("feller bunchers") have achieved wide acceptance in the forest industry. Such machines typically have a crawler type undercarriage for mobility over uneven terrain, a superstructure attached to the undercarriage and an extendable boom attached to the superstructure. The superstructure typically houses an engine and hydraulic pump system to operate the machine's moving parts and generally comprises a cab from which the machine operator controls the machine. Accessories such as grapples, tree falling heads, cut off saws, or de-limbing devices are typically mounted to the boom. The superstructure is typically mounted to the undercarriage on a pivot so that the superstructure and boom can be swung about a vertical axis.
Tree harvesting machines of the type described above are often used off-road on uneven terrain. Therefore, when the vehicle has been driven to a desired position to do work the undercarriage of the vehicle may not be horizontal. It is highly desirable, however, for the comfort of the operator and for the most efficient functioning of the machine that the superstructure of the machine be horizontal while the machine is working. Furthermore, in general, the trees which the machine harvests grow essentially vertically. When the machine is used to handle standing trees, as opposed to previously cut trees, and the superstructure is maintained horizontal while the machine is working then a boom-mounted accessory can be designed to work on a vertical tree without the need for an additional mechanism to tilt the accessory to align with the tree. Accordingly, it has been found to be useful to mount a tilting mechanism between the superstructure of the machine and the undercarriage. The operator of the machine can adjust the tilting mechanism to keep the super structure horizontal even when the undercarriage of the machine is inclined at a significant angle to the horizontal.
Early tilting mechanisms only provided for rotation about a single axis. These tilting mechanisms are called "two-way" tilting mechanisms because they allow the angle of tilt to be adjusted in two directions about the single axis. To maintain the superstructure of a machine equipped with a two-way tilting mechanism horizontal the operator of the machine must orient the machine with the tilting axis perpendicular to the fall line of the ground under the machine's undercarriage. A two-way tilting mechanism cannot generally maintain the superstructure of a machine horizontal when the tilting axis is not horizontal.
So called "four way" tilting mechanisms allow the superstructure of a machine to be tilted back and fourth about each one of a pair of mutually perpendicular axes. A four-way tilting mechanism is therefore capable of maintaining the superstructure of a machine level independently of the direction of inclination of the undercarriage.
Conventional prior art tilt mechanisms have pin joints which permit pivotal motion about the pivot axes of the tilt mechanism. In a pin joint a first member pivots relative to a second member about one or more pivot pins which lie along a pivot axis. In a typical pin joint a projection extends from the second member between two parts of the first member. A hole passes through the projection. The pivot pin extends through the hole in the projection and extends into holes in the first member on either side of the projection. Suitable bushings are provided between the pin and the first and or second members to allow the second member to pivot relative to the first member about the pivot pins.
A problem with pin joints as described above is that it is difficult to eliminate end play in the joint. That is, it is difficult to desig the joint in a way which prevents the projecting part of the second member from moving from side to side along the pivot pin between the two parts of the first member.
When a pin joint is used to form the tilt axis in the tilt mechanism of a heavy piece of machinery, such as a tree harvesting machine, the end play in the pin joint can cause significant problems. It is difficult to make such tilting mechanisms in a manner which prevents motion of the superstructure of the machine relative to the undercarriage in a direction parallel to the pivot axes.
In a tree harvesting machine very large alternating forces are applied to the superstructure of the machine when the boom is extended and retracted and when the superstructure is swung back and forth about its vertical swing axis. If these forces are directed parallel to the axis of one of the pin joints in the tilting mechanism of the machine then the forces can cause the superstructure to move relative to the undercarriage along the pin joint's pins until the end play in the joint is taken up. When the end play is completely taken up the member connected to the superstructure, which forms one half of the pin joint, hammers against the member connected to the chassis of the machine, which forms the other part of the pin joint. Repeated hammering on the pin joints can cause the components of the joints to become fatigued and can lead to premature failure of the machine. Furthermore, the hammering causes vibration throughout the machine which makes the machine noisy and uncomfortable for the operator and can harm components of the machine.